MONTPELIER — The Vermont House on Thursday passed a measure calling for a study of marijuana legalization, while a Senate committee struggled to find a standard to determine when a driver is impaired by drugs.

If the Senate and Gov. Peter Shumlin agree, the legalization study would be focused mainly on the fiscal impact of regulating and taxing marijuana. Shumlin has said he would consider that idea in a future legislative session but wants to see first how legalization works out for the two states that have done so by referendum, Colorado and Washington.

The House gave the measure final passage on a voice vote with no debate. Most of the debate came Wednesday, when it was up for preliminary approval.

Supporters argued that the study, to be completed by the state Agency of Administration by Jan. 15, was for informational purposes only and that voting for it should not be construed as support for marijuana legalization.

Rep. Kurt Wright, R-Burlington, wasn’t buying it.

“A formal study endorsed by the Legislature sends the message to Vermonters that we are indeed taking the first step to legalization of marijuana,” he said as he explained his vote against the study.

The amendment came on a bill making adjustments to an existing state law allowing some sick Vermonters to be prescribed marijuana for relief of their symptoms. Lawmakers said it should not be called “medical marijuana,” because there’s disagreement in the medical community about its efficacy, and it hasn’t been approved by the U.S. Food and Drug Administration.

Existing law limits the number of patients who can receive marijuana to 1,000; the House bill would lift that cap. The House disagreed with a Senate version increasing the number of marijuana dispensaries serving patients from four to six; the differences may have to be worked out in a legislative conference committee.

The bill would allow distribution by the dispensaries of “Charlotte’s Web,” a hemp-based oil said to reduce seizures in some patients with epilepsy.

Part of the study called for by the Vermont House would look at the experiences in Colorado and Washington.

Meanwhile, the Senate Judiciary Committee on Thursday struggled to come up with standards for determining when drivers are impaired by marijuana and other drugs.

Committee members agreed there is not currently an objective standard for when someone is intoxicated by drugs other than alcohol, with which a person is considered drunk if they have a blood-alcohol content of .08 percent or more.

The debate, left unresolved at the end of Thursday’s committee discussion, centered on what would have to be established to prove someone is under the influence of drugs while driving. Some committee members argued that there can be levels of drugs in the body low enough that a driver should not be considered impaired.

Public Safety Commissioner Keith Flynn told the committee he wants a standard of proof that shows a defendant was impaired “to the slightest degree.” He said such a standard is needed for a charge to stick.